"Protesters described by state media as 'students' broke into the British embassy in Tehran today, some throwing stones and 'petrol bombs' and others getting inside and destroying documents. There were also reports of an attack on a second British diplomatic compound.
"This follows the vote by Iran's parliament on Sunday to further reduce ties with the U.K. because of Britain's support for tighter sanctions on Iran due to its suspected pursuit of nuclear weapons."
But at the ceremony in Tehran today, Hammond described that as a "low point" in relations between the U.K. and Iran, but said that since the election of President Hassan Rouhani they had "steadily improved, step by step."
"Today's ceremony marks the end of one long journey, and the start of a new, and, I believe, exciting one," he said, adding that reopening the embassy was the "logical next step to build confidence and trust between two great nations" after last month's nuclear agreement, according to The Associated Press.
"Over the coming months, we will work to ensure that the nuclear agreement is a success, including by making sure that it is fully implemented by all sides," Hammond said.
Iran's Foreign Minister Mohammad Javad Zarif said the reopening of the diplomatic compound showed that Iran has a "constructive role" to play in the region and around the world.
"Of course, we have differences with some European countries but that can be negotiated through interaction, with open eyes and a realistic approach," Zarif said.